1. Field of the Invention
The present invention relates to digital mobile communication equipment provided with a Speech Coder and Decoder, and particularly to the processing of voice signals at low levels which approximate that of background noise.
2. Description of the Related Art
FIG. 18 is a block diagram illustrating part of known mobile communication equipment. Referring to this Figure, reference numeral 1 denotes a microphone for inputting a voice for the mobile communication equipment 100; reference numeral 2 denotes an A/D conversion section for converting analog voice signals into digital voice signals; reference numeral 3 denotes a speaker for outputting voice signals; and reference numeral 4 denotes a D/A converter for converting digital voice signals into analog voice signals.
Reference numeral 5 denotes a digital voice signal processing section comprising a voice coding section 8 for coding digital voice signals, a forward error correction (FEC) coding section 9 for performing forward error correction coding, a forward error correction decoding section 10 and a voice decoding section 11 for decoding received coded digital signals.
Reference numeral 6 denotes a time division multiple access (TDMA) timing control section for controlling the timing for time division multiple access; and reference numeral 7 denotes a control section for controlling the entire mobile communication equipment 100, the control section including a CPU and program for operating the CPU, etc.
Next, the operation will be described according to the Figure. Here, common operations of the mobile communication equipment, such as wireless signal transmission and reception, are not particularly related to the present invention, and therefore explanation thereof is omitted.
When communicating by using the mobile communication equipment 100, first, voice is input from the microphone 1, and the analog voice signals are converted into digital voice signals by the A/D conversion section 2. The digital voice signals are coded by the digital voice signal processing section 5, and the information coded by the digital voice signal processing section 5 is transmitted by the control section 7 for controlling the entire mobile communication equipment 100 and the time division multiple access timing control section 6.
Next, regarding receiving, only the voice information is extracted from the transmitted information by the time division multiple access timing control section 6 and the control section 7, and is input to the digital voice signal processing section 5 where the information is decoded, and the digital voice signals are converted into analog voice signals by means of the D/A converter 4, thereby outputting voice from the speaker 3.
Since the known mobile communication equipment is constructed as described above, both background noise and voice signals at a level as low as the background noise are transmitted to the receiving party along with the actually necessary voice signals, decoded, and output from the speaker as voice signals. Consequently, and particularly in the case where a high-sensitivity microphone is employed, background noise and voice signals at a level as low as the background noise are mixed into the voice signals, making for a problem where it becomes very difficult to hear the voice signals.
The present invention has been are achieved to solve the above-described problems. It is an object of the present invention to provide mobile communication equipment capable of controlling the noise level of voice signals which are being transmitted or received during communication, and reducing irritating sounds for the receiving party.
In light of the above object, according to a first aspect of the present invention, there is provided digital mobile communication equipment provided with a Speech Coder and Decoder, the mobile communication equipment comprising: an A/D conversion feature for converting analog voice signals into digital voice signals; voice coding feature for calculating the voice power value of the digital voice signals from the A/D converter and outputting the aforementioned digital voice signal as it is when the voice power value is equal to or greater than a predetermined value and for outputting the aforementioned digital voice signal as zero when the voice power value is smaller than the predetermined value; and forward error correction coding feature for inputting the coded digital voice signals from the coding feature and for outputting the coded digital voice signals on which forward error correction coding has been performed.
According to a second aspect of the present invention, there is provided digital mobile communication equipment according to the first aspect of the invention, wherein the aforementioned coding feature comprises: a voice power calculating section for calculating the voice frame power value of the digital voice signals from the aforementioned A/D converter as voice power value; a noise level comparing section for outputting the aforementioned digital voice signal as it is when the voice power value is equal to or greater than a predetermined value and for outputting the aforementioned digital voice signal as zero when the voice power value is smaller than the predetermined value; and a voice coding section for outputting the aforementioned digital voice signals output by the noise level comparing section as voice-coded digital voice signals.
According to a third aspect of the present invention, there is provided digital mobile communication equipment according to the first aspect of the invention, wherein the aforementioned coding feature is comprises: a voice coding section for calculating the R0 value from VSELP processing of the digital voice signals from the aforementioned A/D converter as voice power value, which then conducts voice coding processing from the voice power value and outputs the coded digital voice signal when the voice power value is equal to or greater than a predetermined value, and takes the voice power value to be zero when the voice power value is smaller than the predetermined value so that no voice coding processing is conducted.
According to a fourth aspect of the present invention, there is provided digital mobile communication equipment according to the first aspect of the invention, wherein the voice coding section outputs coded digital voice signals for generating comfort noise when the voice power value is smaller than the predetermined value.
According to a fifth aspect of the present invention, there is provided digital mobile communication equipment according to the fourth aspect of the invention, wherein the aforementioned coding feature comprises: a voice coding section for converting digital voice signals from the aforementioned A/D conversion means into coded digital voice signals; and a coded power comparison section for calculating the R0 value based on VSELP algorithms of the coded digital voice signals from the voice coding section as voice power value, which then outputs the aforementioned coded digital voice signal as it is when the voice power value is equal to or greater than a predetermined value, and outputs coded digital voice signals for generating comfort noise when the voice power value is smaller than the predetermined value.
According to a sixth aspect of the present invention, there is provided digital mobile communication equipment provided with a Speech Coder and Decoder, the mobile communication equipment comprising: forward error correction decoding feature for performing forward error correction decoding to received coded digital voice signals and outputting the decoded coded digital voice signals thereof; decoding feature for calculating the voice power value regarding the coded digital voice signals from the forward error correction decoding feature and outputting the digital voice signal decoded as it is from the coded digital signal when the voice power value of the coded digital voice signals is equal to or greater than a predetermined value, and for outputting signals as a voice power value of zero when the voice power value is smaller than the predetermined value; and D/A converting feature for converting digital voice signals output from the decoding feature into analog voice signals.
According to a seventh aspect of the present invention, there is provided digital mobile communication equipment according to the sixth aspect of the invention, wherein the aforementioned decoding feature comprises: a voice decoding section for outputting digital voice signals decoded from the coded digital voice signals from the aforementioned forward error correction decoding feature; a voice power calculating section for calculating the voice frame power value of the digital voice signals from the voice decoding section as voice power value; and a noise level comparing section for outputting the aforementioned digital voice signal as it is when the voice power value is equal to or greater than a predetermined value and for outputting the digital voice signal as zero when the voice power value is smaller than the predetermined value.
According to an eighth aspect of the present invention, there is provided digital mobile communication equipment according to the sixth aspect of the invention, wherein the aforementioned decoding feature comprises: a coded power comparison section for calculating the R0 value based on VSELP algorithms of the coded digital voice signals from the aforementioned forward error correction decoding feature as voice power value, and then compares the voice power value with predetermined values; and a voice decoding section which conducts voice decoding processing from the voice power value and outputs the digital voice signal when the voice power value is equal to or greater than a predetermined value, and takes the voice power value to be zero when the aforementioned voice power value is smaller than the predetermined value so that no voice decoding processing is conducted.
According to a ninth aspect of the present invention, there is provided digital mobile communication equipment according to the sixth aspect of the invention, wherein the voice decoding section outputs digital voice signals for generating comfort noise when the voice power value is smaller than the predetermined value.
According to a tenth aspect of the present invention, there is provided digital mobile communication equipment according to the ninth aspect of the invention, wherein the aforementioned coding feature comprises: a coded power comparison section for calculating the R0 value based on VSELP algorithms of the coded digital voice signals from the aforementioned forward error correction decoding feature as voice power value, which then outputs the aforementioned coded digital voice signal as it is when the voice power value is equal to or greater than a predetermined value, and outputs coded digital voice signals for generating comfort noise when the voice power value is smaller than the predetermined value; and a voice decoding section for decoding coded digital voice signals from the aforementioned coded power comparison section.